How to Get Custom field (Dropdownl list ) selected value?

We have written one dropdown list name['EMployee']. In Employee Field there are 4 employee name ex{john, mark, sham, george}. Suppose we select 'mark' in dropdownlist. Then how should i get value of this field using groovy script?. We need 'mark' string value. Can any one help us. we are using 7.3.0 jira version. Thanks in advance.